Lightweight polyethylene film for aseptic packaging applications and the product resulting therefrom and the process of making the same

ABSTRACT

A multilayer foam film comprising high density polyethylene for direct and non-direct food contact and aseptic packaging application is disclosed. In an embodiment, the film has a bulk density of less than 0.962 gr/cm3 wherein more than 50% of the cells in the foam layer are closed cells. In an embodiment, the foam films are thick (generally more than 8 mils thick) and have a bending stiffness value of more than 18, in Taber stiffness unit configuration according to TAPPI/ANSI T 489 om-15, and the ratio of the mass per unit area (the mass of a unit area of the film in gram per meter-squared (gr/m2)) over the stiffness value in Taber unit configuration is equal to or less than 13. In an embodiment, the film has a very smooth surface with a smoothness value of less than 25 in Sheffiled smoothness unit configuration according to TAPPI T 538. The described foam film can have a water vapor transmission rate value of less than 1 gr/m2/24 hr, according to ASTM E398-13. The described foam film can have an oxygen transmission rate value of less than 10 cc/m2/24 hr, according to ASTM D3985.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/875,198, filed May 15, 2020, which claims priority to U.S.provisional patent application No. 62/849,329 filed on May 17, 2019,each of which is incorporated herein by reference in its entirety.

FIELD

This invention relates to a multilayer foam film of high densitypolyethylene (HDPE) which may be used for paper replacement applicationsin the aseptic packaging industry.

BACKGROUND

Paperboards consumption for packaging applications accounts for almostone-third of the total packaging market. For the direct food contactpackaging, paper boards work safely with a barrier coating of some form.Conventionally, for the food packaging applications where the barrierproperties are essential, the paper boards are paraffin wax coated orlaminated with a polymer film, which is usually polyethylene. For theshelf-stable products that are stored at room temperature, and thepackaging is done aseptically followed by hermetic sealing, oxygenbarrier property is essential. The advent of paper-foil-plasticlaminated containers, e.g., Tetrahedron in 1959, was an inflection pointin packaging industries where it could be replaced with metal cans andglass containers. So, typically a layer of a metalized polymer film oraluminum film is incorporated in the structure of the paperboard. Thiscan cause a significant recycling issue because the vast majority of therecycling sites are deficient in infrastructure that can provide acertain recycling technology. There has been cumulative popularity andinterest for the sterilized and pasteurized products that are beingpackaged aseptically which eliminates refrigeration and preventsspoilage without using preservatives, for example, milk, baby foods,tomato products, broths, soups, vegetables, desserts, liquid egg,yogurt, dressings, etc. So, with the vast demand growth in foodpackaging in emerging markets, it would be desirable to produce alightweight recyclable polymeric film that possesses surface quality forprinting and preprinting shelf life, bending stiffness values comparableto the paperboards used in packaging, and sufficient barrier properties,all of which may be essential attributes for a product to replace thekinds of paperboard currently being used in packaging industries.Moreover, the mentioned product can address the wicking issues of coatedpaperboards.

To the best of applicant's knowledge, no recyclable lightweight film ofpolyethylene has been disclosed in the prior art to replace paperboards,coated paperboards, or laminated paperboards in food packagingindustries that can possess all the aforementioned attributes such ashigh surface smoothness, high enough bending stiffness, high oxygen andmoisture barrier properties, relatively low coefficient of friction onthe skin layer, and which can address anti-static charge issues in theindustrial packaging process.

SUMMARY

A recyclable lightweight multilayer film which may be used for asepticpackaging application is described herein. The film can have a verysmooth surface resulting in superior printing quality and high enoughbending stiffness to replace paper boards.

In one aspect, a coextruded lightweight multilayer thermoplastic film isprovided. The film comprises at least one foam layer including aplurality of cells wherein at least 10% of the cells are closed cells.The film further comprises two solid skin layers comprising HDP. Thefilm further comprises one or more solid layer, comprising Ethylenevinyl alcohol (EVOH), each between the foam layer and solid layer, orbetween two of the solid layers, or between two of the foam layers. Thefilm has an overall thickness equal to or greater than 8 mils, and abending stiffness value of greater than 18 in Taber stiffness unitconfiguration according to TAPPI/ANSI T 489 om-15. The ratio of the massper unit area (the mass of a unit area of the film in gram permeter-squared (gr/m²)) over the stiffness value in Taber unitconfiguration is equal to or less than 13.

In another aspect, a coextruded lightweight multilayer thermoplasticfilm is provided. The film comprises at least one foam layer including aplurality of cells wherein at least 10% of the cells are closed cells.The film further comprises solid skin layers comprising HDPE. The filmfurther comprises one or more solid layer, comprising Ethylene vinylalcohol (EVOH), each between the foam layer and solid layer, or betweentwo of the solid layers, or between two of the foam layers. The film hasan overall thickness equal to or greater than 8 mils. The film has anaverage Sheffield smoothness of less than 40, according to TAPPI T 538.In some embodiments, more than 50% of the cells are closed cells.

The film can have a bending stiffness value of more than 18, in Taberstiffness unit configuration according to TAPPI/ANSI T 489 om-15,wherein the ratio of the mass per unit area (the mass of a unit area ofthe film in gram per meter-squared (gr/m²)) over the stiffness value inTaber unit configuration is equal to or less than 13.

The film can have a surface with an average Sheffield smoothness,according to TAPPI T 538, of less than 25.

In some embodiments, the film can have an oxygen transmission rate ofless than 0.65 cc/100 in²/24 hr, or 10 cc/m²/24 hr, according to ASTMD3985.

In some embodiments, the film can have a water vapor transmission rateof less than 0.05 gr/100 in²/24 hr, according to ASTM E398-13.

Other aspects, embodiments, advantages, and features will becomeapparent from the following detailed description.

DETAILED DESCRIPTION

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

All ranges disclosed herein are inclusive of the recited endpoint andindependently combinable (for example, the range of the bendingstiffness in Taber unit configuration from 18 to 100″ is inclusive ofthe endpoints, 18 and 100, and all the intermediate values. In the samecontext, for example, the overall thickness of greater than 8 mils isinclusive of the endpoint, 8 mils.)

As used herein, approximating language may be applied to modify anyquantitative representation that may vary without resulting in a changein the basic function to which it is related. Accordingly, a valuemodified by a term or terms, such as “about” and “substantially,” maynot be limited to the precise value specified. The modifier “about”should also be considered as disclosing the range defined by theabsolute value of the two endpoints. For example, the expression “fromabout 0.05 to about 15” also discloses the range “from 0.05 to 15”.

As used herein, the term “lightweight” refers to the bulk density valueof the products described herein being less than, or equal to, thedensity of their solid counterpart made from the associated base virginresin, or the density of the associated base virgin resin. In a similarcontext, it refers to the bulk density value of the products describedherein being less than, or at least equal to, the density of thepaperboards with the same thickness or with the same weight values perunit area in gr/m². For example, bulk density values of the products ofthis invention can be less than 0.962 gr/cm³ which is less than thedensity value of the associated base virgin resin of 0.962 gr/cm³, orless than the bulk density value of 0.962 gr/cm³ of its solidcounterpart made from the associated base virgin resin.

The present disclosure relates to multilayer lightweight polyethylenefoam film suitable to be used in all sorts of aseptic packaging;packaging of all sorts of oxygen-sensitive products, packaging ofpasteurized products; packaging of dry food products such as biscuits,cookies, cereals, tea, coffee, sugar, flour, dry food mixes, chocolates,sugar confectionaries, pet food; packaging of frozen foods such aschilled foods and ice creams; packaging of cooked and precooked productsand foods; backing board for fresh products such as vegetables, fruits,meat and fishes; packaging of baby foods; packaging of all kinds ofdesserts; packaging of liquid food and beverages such as broths, soups,juice drinks, milk and all sorts of products derived from milk,concentrates, all kinds of dressing, liquid eggs, tomato products; andpackaging of all kinds of laundry detergents, shampoos, and body washes;making all sorts of pouches to include SUP, sachets, and packaging ofpet foods.

The abovementioned examples do not put any limitation on the applicationof the products of this disclosure, and other applications may bepossible.

One of the rationales behind the production of the synthetic lightweightfilms described herein and material selection for paperboard replacementis to address the recyclability, and to avoid the drawbacks of using thewax-coated paper boards, metalized films, and the films and sheets withan aluminum layer all of which are either not recyclable or cannot berecycled easily; although in reality the vast majority of the consumersintuitively believe that the above-mentioned products, such asaseptically-packaged milk boxes or long-shelf life beverage boxes, arerecyclable.

Herein a recyclable lightweight multilayer film is disclosed which, insome embodiments, comprises no less than five layers, e.g., sevenlayers, to be a replacement for paper boards that are being used inpackaging industries, e.g., for aseptic packaging applications, and fordirect and non-direct food contact packaging application. The filmcomprises high-density polyethylene (HDPE) wherein at least one layer,excluding the solid skin layers, has a cellular structure. In someembodiments, at least 10% of the cells are closed-cell; in someembodiments, more than 50% of the cells are closed cells; and, in someembodiments, more than 75% of the cells are closed cells. As usedherein, a “closed cell” refers to a cell that has cell walls thatcompletely surround the cell with no openings such that there is nointerconnectivity to an adjacent cell. In some embodiments, the filmcomprises at least one solid layer containing EVOH, each of whichlocated somewhere between the foam layer and solid layer, or between twoof the solid layers.

In some embodiments, the mass concentration of the EVOH in every unitarea of the multilayer film is less than 5 percent of the mass of theunit area of the film. In some embodiments, the mass concentration ofthe EVOH in every unit area of the multilayer film is less than 5percent of the mass of the unit area of the film. In some otherembodiments, the mass concentration of the EVOH in every unit area ofthe multilayer film is less than 2 percent of the mass of the unit areaof the film.

Furthermore, the bending stiffness of the disclosed multilayer foamedfilm product could be improved over their solid counterparts to fulfillthe property requirement in packaging industries. This could be donefirst and foremost by the inclusion of one or more cellular layer in thecore of the multilayer film or between two solid skin layers, anaccurate tune and alteration of the thickness of the cellular layer aswell as fine-tuning the thickness of the solid skin layers. Generally,at the same thickness, a solid film of polyethylene can hardly possessbending stiffness values that paperboards can offer. This is due to thehigh degree of fiber alignment in paperboard which can significantlyenhance the bending stiffness. In addition, it might be due to higherinherent stiffness of the individual fibers in the paperboard comparedto the polymer chains in the polymeric film.

In general, HDPE owns a relatively low water vapor transmission rate ofabout 0.3-0.5 (g/100 in²/24 hr). Embodiments of the multilayer foamedfilm products described herein can exhibit significantly higher moisturebarrier properties compared to its solid counterparts with the samevalue of mass per unit area (in gram per meter squared). Also,embodiments of the multilayer foamed film products described herein canexhibit an enhanced oxygen barrier property.

Also, one of the issues in industrial-scale use of the polymericpackages, which can be a crucial factor in the efficient andcost-effective packaging process, is the ability of them to be de-nestedquickly and freely. De-nesting problems are typically due to thefriction and static charge. Embodiments of the multilayer foam filmsdescribed herein can exhibit an anti-static and low friction behavior bymanipulating the skin layer's structure and by the inclusion ofappropriate amounts of slip agents, anti-block and anti-static agentinto the solid skin layer.

One of the steps for making the disclosed product is how the bendingstiffness may be controlled and enhanced by the inclusion andcontrolling the thickness of the core cellular layer, or the cellularlayers between the two skin layers, and fine-tuning the solid skins, aswell as how the surface smoothness has been enhanced significantly byadding a tiny amount of supercritical blowing agent. Moreover, how theunique structure and layer combination has resulted in a high barrierproperty without the inclusion of an aluminum or metalized barrierlayer. That is, the film product may be free of any metal (e.g.,aluminum) barrier layer.

In some embodiments, a blown film process may be used where the headpressure of the extruder can go high because of a very narrow gap thatbenefits the nucleation of cells in the foam layer. Using such atechnique, the melt fracture should be avoided, and the resin shouldhave excellent thermal stability and high enough melt strength.Typically, film manufacturers capitalize on a blend of a low-densitypolyethylene (LDPE) and a linear low-density polyethylene (LLDPE), whilethe blend is an immiscible blend in many cases, wherein LDPE can improvethe processing ability and ductility while the LLDPE can enhance themodulus and strength. In some embodiments, all layers of the describedmultilayer film comprise HDPE and, in some cases, the polymeric materialin one or more of these layers consists essentially of HDPE and, in somecases, the polymeric materials in at least one of the solid layers,excluding the solid skin layers, comprises EVOH. In one embodiment, atleast one layer of the multilayer film can comprise LDPE.

In some embodiments, the multilayer film can be comprised of ninelayers; in some embodiments, seven layers; and, in some embodiments,five layers. For example, a five-layer film may comprise a foam corelayer (e.g., comprising HDPE) and at least two solid layers (e.g.,comprising HDPE), each one on respective opposite sides of the corelayer, and at least one solid layer (e.g., comprising EVOH), each onebetween the foam layer and solid skin layer.

In one case, a seven-layer foam film comprises a foam core layer (e.g.,comprising HDPE) in the middle with two solid skin layers on eachopposite side of the core layer, and at least one solid layer (e.g.,comprising EVOH), each one between the foam layer and solid skin layer.In another case, a seven-layer foam film comprises a solid core layer(e.g., comprising EVOH) in the middle with two solid skin layers on eachopposite side of the core layer, and at least one foam layer (e.g.,comprising HDPE), each one between the solid core layer and the solidskin layer.

In another embodiment, a nine-layer foam film comprises a foam corelayer (e.g., comprising HDPE) in the middle with two solid skin layerson each opposite side of the core layer, and at least one solid layer(e.g., comprising EVOH), each one between the foam layer and solid skinlayer. In another embodiment, a nine-layer foam film comprises a solidcore layer (e.g., comprising EVOH) in the middle with two solid skinlayers on each opposite side of the core layer, and at least one foamlayer (e.g., comprising HDPE), each one between the solid core layer andsolid skin layer.

In another embodiment, the multilayer film, which can be five, seven, ornine layers, comprises at least one foam layer and two solid skinlayers, and at least one solid layer (e.g., comprising EVOH). In anotherembodiment, the multilayer film, which can be five, seven, or ninelayers, comprises at least one solid layer, comprising EVOH, each ofwhich located between the foam layer and solid layer, or between the twosolid layers.

In some embodiments, the multilayer film described herein comprisesmultiple layers, e.g., from 3 layers to 9 layers, comprising at leastone foam layer and one or more solid layers containing EVOH. In someother embodiments, the multilayer film described herein comprisesmultiple layers, e.g., from 3 layers to 9 layers, comprising at leastone solid layer containing EVOH.

It should be understood that other layer configurations may be possible.

In one embodiment, the process to produce the described multilayer filmsmay utilize a very small and precise amount of supercritical gas, forexample, below 0.1 wt %, as a processing aid and blowing agent. In someembodiments, other gas concentrations, e.g., more than 0.1 percent byweight maybe possible. Such supercritical gas may be injected into themolten polymer at a high pressure, for example, greater than 34 bar,inside an efficient and effectual mixer, e.g., cavity transfer mixer, asan extension to the extruder's barrel. The supercritical blowing agentused in the process can be either nitrogen, carbon dioxide, or a mixtureof nitrogen and carbon dioxide. In some embodiments, the supercriticalblowing agent can be introduced inside the mixing section of theextruder at the injection pressure greater than or equal to 34 bar; insome cases, greater than or equal to 70 bar; in some cases, greater thanor equal to 240 bar, and, in some cases, greater than or equal to 380bar. The temperature of the mixer could be accurately controlled within±1° C. The inclusion of a tiny amount of gas can offer a few importantadvantages in the process and, for example, blown film extrusionprocesses. For example, the gas can reduce the back pressure whichallows processing at higher throughput and can delay any bubbleinstability. Therefore, melt fracture could be reduced significantly.Also, the gas can enhance the processing ability of the HDPE, and toserve as a physical blowing agent with the presence of a nucleatingagent in the layer that has a cellular structure. The addition of thephysical blowing agent can depress the development of melt fracture dueto the viscosity manipulation of the melt which may result in highsurface smoothness. Hence the printing quality on the film can beimproved significantly.

In general, conventional polymer processing equipment may be used toproduce the films described herein. In some cases, for example, the filmcan be produced by the blown film process using an annular die with adie gap from 0.45 to 1.3 mm and a blow-up ratio ranging from 1.5:1 to3.5:1. Higher blow-up ratios might result in a more balanced MD/TD(machine direction/transverse direction) orientation, which improvesoverall film toughness. The die geometry and specification may bemanufactured according to, for example, the patent application US2012/0228793 A1, which is incorporated by reference herein in itsentirety.

The majority of the conventional PE blown films are processed using a PEblend comprising LDPE for enhancing bubble stability. Almost all theHDPE films are made in a high stock blown film process; otherwise, thetear strength of the HDPE film deteriorates significantly. As describedabove, in embodiments of the methods are used for producing themulti-layer films, a supercritical gas may be injected into the melt ata precisely controlled rate, inside a transfer mixer, before enteringthe annular die. This unit could be controlled as a separate temperaturezone with an accuracy of ±1° C. and a gas injection pressure variationbelow 1%. The plasticization effect of the gas can result in a viscositychange of the molten resin which would enhance the processing ability ofthe resin inside the annular die at a lower temperature compared to theprocessing temperature which is being used conventionally. Hence, arelatively stable bubble can be made inside the pocket. Then, because ofthe overall high specific heat capacity of polyethylene, the transversestretch of the bubble can be delayed until the film becomes cooler,which may further enhance the bubble stability and the frost lineheight. This also might be beneficial in manipulating thecrystallization kinetics of the skin layers to improve a few otherphysio-mechanical properties. The higher degree of crystallization inthe skin might lower the coefficient of friction on the skin layers.

In some embodiments, the multilayer foam films described herein can beproduced by the blown film process, cast film process, or other suitablemethods.

In some embodiments, the polymer composition of each layer comprisessome apt amounts of other additives, such as pigments, slip agents,antistatic agents, UV stabilizers, antioxidants, nucleating agents,clarifying agents, or maleic anhydride. The foam layer optionally maycontain 0.05 to 15 percent by weight of an inorganic additive, anorganic additive or a mixture of an inorganic and an organic additive asa nucleating agent. For example, the foam layer may contain up to about15% by weight of talc as a nucleating agent. In some embodiments, atleast one layer may include a clarifying agent at less than 1 percent byweight, such as less than 0.5 percent by weight, such as less than 0.1percent by weight, such as less than 0.05 percent by weight. In somecases, at least one layer of the film may contain up to about 35 wt % ofcalcium carbonates.

In some embodiments, at least one layer of the film described hereincomprise less than 5 percent by weight maleic anhydride, for example,less than about 2 percent by weight.

In some cases, multilayer foam film can be comprised of two solid skinlayers wherein one of the skin layers contains an apt amount of blackpigments, for example, less than 1 percent by weight, and the othersolid skin layer contains apt amounts of white pigments, for example,less than 1 percent by weight. In some other embodiments, both solidskin layers comprise an apt amount of white pigments.

In another case, the solid skin layers of the multilayer foam filmcomprise less than 0.5 percent by weight of an anti-blocking agentand/or less than 0.2 percent by weight of an anti-static agent.

In one embodiment, the multilayer foamed film has at least one solidskin layer with a static coefficient of friction value of less than 0.4,such as less than 0.38. In another embodiment, the film has at least onesolid skin layer with a dynamic coefficient of friction value of lessthan 0.3.

The described multilayer film, comprising at least one foam layer, mayhave sets of significantly improved physiomechanical properties comparedto known foamed film articles as in particular the bending stiffnessvalue of greater than 18, in some cases greater than 20, and in somecases, greater than 25, all in Taber stiffness unit configuration,according to TAPPI/ANSI T 489 om-15, wherein the ratio of the mass perunit area (the mass of a unit area of the film in gram per meter-squared(gr/m²)) over the stiffness value in Taber unit configuration is equalto or less than 13; in some cases, less than 11, and, in some cases,less than 10. In an embodiment, the film can have a Taber bendingstiffness value of less than 280, according to TAPPI/ANSI T 489 om-15.

The described films can have a surface with an average Sheffieldsmoothness, according to TAPPI T 538, of less than 100. In someembodiments, the film may have an average Sheffield smoothness of lessthan 50; in some cases, less than 40; in some cases, less than 30; and,in some cases, less than 15.

The multilayer foam film can have an overall thickness of greater than 8mils, in some cases, greater than 10 mils, in some cases, greater than13 mils, and in some cases greater than 15 mils.

In some embodiments, the lightweight film of this invention has a bulkdensity less than 1 gr/cm³; in some cases, less than 0.962 gr/cm³; insome cases, less than 0.94 gr/cm³; in some cases, less than 0.9 gr/cm³;in some cases, less than 0.85 gr/cm³; and in some cases, less than 0.8gr/cm³.

In some embodiments, the foam layer of the disclosed film has a farbetter cellular morphology compared to the known films. For example, thefoam layers of the disclosed films can have uniformly distributed cells,for example with a closed-cell morphology, an average cell size of about10-250 μm, an average cell density with respect to the un-foamed polymervolume of about 10²-10⁹ cells/cm³, and an expansion ratio of the foamedlayer from 1 to 9. In some cases, the foam layer comprises at least 10%closed cells and, in some cases, more than 50% closed cells. In oneembodiment, the foam layer has a substantially entirely closed-cellmorphology (e.g., greater than 95% closed cells).

In some embodiments, the multilayer foam film comprises at least onelayer containing the PE/EVOH blend. In some embodiments, the multilayerfoam film described herein comprises at least one layer, excluding thesolid skin layers, containing from about 30 to 50 percent by weight ofEVOH, and less than 5 percent by weight maleic anhydride, e.g., 2percent by weight. In some embodiments, the overall mass concentrationof the EVOH in a unit area of the film does not exceed 5 percent of themass of the unit area of the film.

The films described herein can have a water vapor transmission rate ofless than 0.05 gr/100 in²/24 hr, according to ASTM E398-13. In one case,the water vapor transmission rate of the film is less than 0.1 gr/100in²/24 hr.

In some embodiments, the described film can have an oxygen transmissionrate of less than 0.65 cc/100 in²/24 hr, or 10 cc/m²/24 hr, according toASTM D3985. In one case, the described film can have an oxygentransmission rate of less than 0.32 cc/100 in²/24 hr, or 5 cc/m²/24 hr,according to ASTM D3985.

In some embodiments, the described film comprises at least one layercontaining a resin with an oxygen transmission rate value of less than0.65 cc/100 in²/24 hr, according to ASTM D3985. In another embodiment,the described film comprises at least one layer, excluding the solidskin layers, containing ethylene vinyl alcohol (EVOH).

In an exemplary embodiment, the multilayer foam film, e.g., five-layerfoam film, has at least one solid skin layer with a static coefficientof friction value of less than 0.4, and/or less than 0.38. In anotherembodiment, the film, e.g., five-layer foam film, has at least one solidskin layer with a dynamic coefficient of friction value of less than0.3.

In some embodiments, various thermoplastics can be used in at least onelayer of the multilayer foam film and in the blown film process such aspolyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET),ethylene vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), polyvinylchloride (PVC), Polyvinylidene chloride (PVDC), polyamide (PA), LLDPEcopolymer which include an α-olefin co-monomer such as butene, hexene,or octene; any of the resins known as TPE family such as, but notlimited to, propylene-ethylene copolymer, thermoplastic olefin (TPO),and thermoplastic polyurethane (TPU).

In another embodiment, at least one layer, (e.g., excluding the outerskin layers), of the film may comprise LDPE, PP, PA, EVOH, EVA, or PVOH.The following examples demonstrate the process of the presentdisclosure. The examples are only demonstrative and are intended to putno limit on the disclosure with regards to the materials, conditions, orthe processing parameters set forth herein.

EXAMPLES

All of the products resulting from the examples below were tested andcharacterized in terms of bending stiffness, surface smoothness, oxygentransmission rate, water vapor transmission rate, and density. Tocharacterize the bending stiffness of the film, a TABER StiffnessTester, Model 150-E from Taber Industries, was used. The smoothness ofthe products was evaluated using a Gurley™ 4340 Automatic Densometer &Smoothness Tester. The Oxygen Transmission Rate (OTR) of the productswas measured using OX-TRAN 1/50 tester from AMETEK MOCON, according toASTM D3985. The Water Vapor Transmission Rate (WVTR) of the samples wasmeasured using a PERMATRAN-W Model 1/50 G+ tester from AMETEK MOCON,according to ASTM E398-13.

Example 1: Samples of multilayer HDPE film (seven layers) were producedusing a 7 layer blown film line from Reifenhauser Extrusion Systemequipped with internal bubble cooling system, gauge control, massthroughput control, and layer thickness control, consisting sevenextruders including two 55 mm Extruders denoted as “A” and “G”, for theskins, two 65 mm Extruders denoted as “B” and “F”, and three 35 mmextruders denoted as “C”, “D”, and “E. Both 65 mm extruders wereequipped with supercritical gas injection unit, capable of injectingnitrogen, carbon dioxide, or a mixture of both, as well as two 65 mmMuCell Transfer Mixer (MTM), all from MuCell Extrusion LLC. All thefilms were produced by the blown film process using an annular die witha die gap ranging from 0.7 to 1.2 mm and a blow-up ratio ranging from2.8:1 to 3.5:1. The lip of the annular die was boron nitride coated.

Table 1 contains the processing data, as well as the characterizationresults of the products, which were made, as non-limiting examples toelucidate this invention. The samples were produced with high-densitypolyethylene ELITE 5960 from Dow Chemical Company, having the melt indexof 0.85 dg/min and the density of 0.962 gr/cm³. In all samples, whererequired, the additives, e.g., color pigments, were added in the form ofa masterbatch with LDPE carrier. Obviously, the additives can becompounded in an HDPE carrier. In a few samples, a minor fraction of theLDPE 1321 from Dow Chemical Company with the melt index of 0.25 dg/minand the density of 0.921 gr/cm³ was used. The calcium carbonate and talcwere prepared and introduced as a highly filled masterbatch of,respectively, 80 wt % filled calcium carbonate and 70 wt % filled talcwithin the HDPE as the base carrier resin. All of the tie layerscomprise ADM ER adhesive resin, which is anhydride grafted polyolefin.In this example, the middle layer comprises Ethylene vinyl alcohol(EVOH) with an ethylene content of 32%.

All the samples were coextruded with a total throughput of 300 to 340kg/hr, as it is listed in table 1. The temperature of the mixingsection, wherein the supercritical gas was injected, was kept at 184° C.for all the samples. Supercritical nitrogen was used as a physicalblowing agent and was injected into the MuCell Transfer Mixer (MTM) atthe concentration from 0.01 wt % to 0.07 wt %, very accurately, into themolten polymer. The temperatures of the extruders' zones were setaccording to the conventional processing suggested in the datasheet ofthe materials.

Sample 2 and 3 are the foam versions of the solid sample 1 with the samebasic weight of 342 gr/m², which have 40% and 45% less density comparedto the solid sample 1, respectively.

As it is listed in table 1, sample 3 shows 190% higher bending stiffnessvalue compared to its solid counterpart. Sample 5 and 6 are the foamversions of sample 4 with the same basic weight of about 390 gr/m²,which have 37% and 39% less density compared to the solid sample 4.Samples 5 and 6 show 140% and 160% higher bending stiffness valuescompared to their solid counterpart, respectively. Sample 6 possessesthe surface smoothness value of about 17.5, in Sheffield, which iscomparable to sample 4. Both samples 5 and 6 show an oxygen transmissionrate below 1.5 cc/m²/day.

Samples 8, 9, 10, and 11 are the foam version of sample 7 with a similarbasic weight of about 240 g/m², which has about 20% to 30% less density.Samples 9 and 10 possess 140% and 190% higher bending stiffness comparedto their solid counterpart. Although samples 8 and 9 have much thinner(almost half) middle layer compared to sample 10, they show an oxygentransmission rate in the same range all less than 3 cc/m²/day. Also,samples 8 and 9 have a surface smoothness value of below 10, inSheffield, and comparable to their solid counterpart.

Moreover, almost all the samples 1 to 11 possess a water vaportransmission rate of less than 1 gr/m²/day.

TABLE 1 Sample 1 2 Code Solid 330 #1-0.055N2-330 ID C2-22-01 C2-22-02Density (gr/cm³) 1.284 0.796 Thickness (um) 300 430 Basic weight (gr/m²)342.3 342.3 Total Throughput 300 300 Layers A B C D E F G A B C D E F GHDPE (wt %) 70 50 50 70 70 50 50 70 80% CaCO3 filled 20 20 20 20 PE (wt%) mPE (wt %) 70 70 70 70 Adhesive (wt %) 30 30 30 30 EVOH (wt %) 100100 70% talc filled 25 25 25 25 HDPE (wt %) 64% talc filled 20 20 20 20PE (wt %) LDPE (wt %) 5 10 10 5 5 10 10 5 SC-N2 (%) 0.055 0.055 LayerThickness (um) 55 82 8 10 8 82 55 55 147 8 10 8 147 55 Throughput(kg/hr) 53.2 85.2 6.4 10.4 6.4 85.2 53.2 53.2 85.2 6.4 10.4 6.4 85.253.2 Bending Stiffness 38.4 (Taber) Smoothness (Sheffield) 14.2 OTR(cc/m2/day) 1.33 WVTR (gr/m2/day) <1 Sample 3 4 Code #2-0.065N2-330Solid 390 ID C2-22-03 C2-22-04 Density (gr/cm³) 0.712 1.19 Thickness(um) 480 330 Basic weight (gr/m²) 342.3 392.6 Total Throughput 300 300Layers A B C D E F G A B C D E F G HDPE (wt %) 70 50 50 70 65 50 50 7080% CaCO3 filled 20 20 30 30 PE (wt %) mPE (wt %) 70 70 70 70 Adhesive(wt %) 30 30 30 30 EVOH (wt %) 100 100 70% talc filled 25 25 25 25 HDPE(wt %) 64% talc filled 20 20 20 20 PE (wt %) LDPE (wt %) 5 10 10 5 10 5SC-N2 (%) 0.065 0.065 Layer Thickness (um) 55 172 8 10 8 172 55 55 90 1510 15 90 55 Throughput (kg/hr) 53.2 85.2 6.4 10.4 6.4 85.2 53.2 47.887.8 10.5 9.1 10.5 87.8 46.4 Bending Stiffness 76.2 50.5 (Taber)Smoothness (Sheffield) 117.2 16.6 OTR (cc/m2/day) 4.17 to 34.2 1.18WVTR(gr/m2/day) 0.93 <1 Sample 5 6 Code #4-0065N@-390 #6 ID C2-22-05C2-22-06 Density (gr/cm³) 0.742 0.718 Thickness (um) 535 540 Basicweight (gr/m²) 396.7 387.9 Total Throughput 340 340 Layers A B C D E F GA B C D E F G HDPE (wt %) 65 50 50 70 65 65 80% CaCO3 filled 30 30 20 20PE (wt %) mPE (wt %) 70 70 70 70 Adhesive (wt %) 30 30 30 30 EVOH (wt %)100 100 70% talc filled 25 25 30 30 HDPE (wt %) 64% talc filled 20 20 2020 PE (wt %) LDPE (wt %) 10 5 5 60 60 5 SC-N2 (%) 0.065 0.065 0.0650.065 Layer Thickness (um) 55 193 15 10 15 193 55 55 97.5 15 10 15 97.555 Throughput (kg/hr) 53.6 100 11.8 10.2 11.8 100 52 54.4 98.3 12.1 10.412.1 98.3 54.4 Bending Stiffness 70.5 80.5 (Taber) Smoothness(Sheffield) 26.7 17.5 OTR (cc/m2/day) 1.45 <1.5 WVTR(gr/m2/day) <1 <1Sample 7 8 Code Solid 243 #1A-F Foam ID C2-18-01 C2-18-02 Density(gr/cm³) 1.174 0.959 Thickness (um) 207 250 Basic weight (gr/m²) 243.1239.8 Total Throughput 340 343.5 Layers A B C D E F G A B C D E F G HDPE(wt %) 65 30 30 65 65 20 20 65 80% CaCO3 filled 30 30 30 30 PE (wt %)mPE (wt %) 70 70 70 70 Adhesive (wt %) 30 30 30 30 EVOH (wt %) 100 10070% talc filled 30 30 30 30 HDPE (wt %) 64% talc filled 20 20 20 20 PE(wt %) LDPE (wt %) 5 20 20 5 5 30 30 5 SC-N2 (%) 0.065 Layer Thickness(um) 45 46.5 8 8 8 46.5 45 44.7 46.2 9.9 4 9.8 90.6 44.8 Throughput(kg/hr) 71.1 82 10.3 13.3 10.3 82 71.1 72.3 82.9 13 6.8 12.9 83.1 72.4Bending Stiffness 15.7 15.8 (Taber) Smoothness (Sheffield) 7 7.3 OTR(cc/m2/day) 1.63 2.47 WVTR (gr/m2/day) <1 0.694 Sample 9 10 Code #1B,F&B Foam #2 ID C2-18-03 C2-18-04 Density (gr/cm³) 0.856 0.842 Thickness(um) 280 300 Basic weight (gr/m²) 239.6 252.7 Total Throughput 342.8 340Layers A B C D E F G A B C D E HDPE (wt %) 65 20 20 65 65 50 80% CaCO3filled 30 30 30 PE (wt %) mPE (wt %) 70 70 70 70 Adhesive (wt %) 30 3030 30 EVOH (wt %) 100 100 70% talc filled 30 30 30 HDPE (wt %) 64% talcfilled 20 20 20 PE (wt %) LDPE (wt %) 5 30 30 5 5 SC-N2 (%) 0.065 0.0650.065 Layer Thickness (um) 44.4 83.5 9.9 4.1 9.8 83.5 44.8 45 89.7 10.510 10.2 Throughput (kg/hr) 71.7 82.8 13 7 12.9 83 72.4 68.4 80.8 13 1612.6 Bending Stiffness 21.8 30.1 (Taber) Smoothness (Sheffield) 5.6 31.7OTR (cc/m2/day) 2.76 3.09 WVTR (gr/m2/day) 0.739 1.07 Sample 10 11 Code#2 #3 ID C2-18-04 C2-18-05 Density (gr/cm³) 0.842 0.81 Thickness (um)300 300 Basic weight (gr/m²) 252.7 243.1 Total Throughput 340 340 LayersF G A B C D E F G HDPE (wt %) 50 65 65 50 50 65 80% CaCO3 filled 30 3030 PE (wt %) mPE (wt %) 70 70 Adhesive (wt %) 30 30 EVOH (wt %) 100 70%talc filled 30 30 30 HDPE (wt %) 64% talc filled 20 20 20 PE (wt %) LDPE(wt %) 5 5 5 SC-N2 (%) 0.065 0.065 0.065 Layer Thickness (um) 89.7 45 4593 8 8 8 93 45 Throughput (kg/hr) 80.8 68.4 71.1 82 10.3 13.3 10.3 8271.1 Bending Stiffness 30.1 (Taber) Smoothness (Sheffield) 31.7 OTR(cc/m2/day) 3.09 WVTR (gr/m2/day) 1.07

Example 2: Samples of multilayer HDPE film (three layers) were producedusing a blown film line from Windmoeller & Hoelscher Corporationcomprising one 105 mm main extruder and two identical 75 mmco-extruders. The core extruder was equipped with a supercritical gasinjection unit, capable of injecting nitrogen or carbon dioxide, and a120 mm MuCell Transfer Mixer, both from MuCell Extrusion LLC. All thefilms were produced by the blown film process using an annular die witha die gap ranging from 0.45 to 1.3 mm and a blow-up ratio ranging from2.8:1 to 3.5:1. The lip of the annular die was boron nitride coated.

Table 2 contains the characterization results of the products (samples12 to 15) were made, as non-limiting examples to elucidate on someembodiments of this invention. The samples were produced withhigh-density polyethylene ELITE 5960 from Dow Chemical Company, havingthe melt index of 0.85 dg/min and the density of 0.962 gr/cm³. Thecalcium carbonate and talc were prepared and introduced as a highlyfilled masterbatch of, respectively, 80 wt % filled calcium carbonateand 70 wt % filled talc within the HDPE as the base carrier resin. Thefoamed core layer of all samples contains talc as the cell nucleatingagent.

All the samples were coextruded with the total throughput of about 260to 290 kg/hr, as it is listed in table 2. The temperature of the mixingsection, wherein the supercritical gas was injected, was kept at 190 °C. for all the samples 12 to 15. Supercritical nitrogen was used as aphysical blowing agent and was injected into the MuCell Transfer Mixer(MTM) at the concentration from 0.011 wt % to 0.02 wt %, veryaccurately, into the molten polymer.

Sample 15 is the solid counterpart of samples 12, 13, and 14 which haveabout 18% to 25% less density compared to sample 15. Sample 15 showed anoxygen transmission rate of less than 1.4 cc/m²/day. All the samplesexhibit a water vapor transmission rate of less than 1, as well as asurface smoothness value of less than 10, in Sheffield.

TABLE 2 Sample 12 13 14 15 ID C2-14-1 C2-14-2 C2-14-4 C2-14-5 Density(gr/cm³) 0.9 0.88 0.826 1.104 Thickness (um) 121 125 155 104.5 Basicweight (gr/m²) 110 110 128 110 Total Throughput 287.2 261 261 261 LayersA B C A B C A B C A B C HDPE (wt %) 68 80 98 68 80 98 68 35 98 68 35 9864% talc filled PE (wt %) 18 18 18 18 70% talc filled HDPE (wt %) 30 3030 30 Maleic anhydride (wt %) 2 2 2 2 EVOH (wt %) 45 45 LDPE (wt %) 2 22 2 2 2 2 2 SC-N2 (%) 0.01 0.01 0.01 <<0.011 Layer Thickness (um) 31.549.1 40.4 24.7 37.2 44.5 29 73.7 52.3 24.9 34.7 44.9 Throughput (kg/hr)91.5 92.2 104 65.3 92.2 104 65.3 92.2 104 65.3 92.2 104 Smoothness(Sheffield) <10 <10 <10 <10 OTR (cc/m2/day) 239 276 6.64 1.38 WVTR(gr/m2/day) 0.571 0.581 0.847 0.86

1. A coextruded lightweight multilayer thermoplastic film comprising: atleast one foam layer including a plurality of cells, wherein at least10% of the cells are closed cells, and solid layers comprising HDPE oneach side of the foam layer, and one or more solid layers, comprisingethylene vinyl alcohol (EVOH), each between the foam layer and the solidlayer, or between two of the solid layers, wherein the film has anoverall thickness equal to or greater than 8 mils, and a bendingstiffness value of greater than 18 in Taber stiffness unit configurationaccording to TAPPI/ANSI T 489 om-15, and the ratio of the mass per unitarea (the mass of a unit area of the film in gram per meter-squared(gr/m²)) over the stiffness value in Taber unit configuration is equalto or less than
 13. 2. A coextruded lightweight multilayer thermoplasticfilm comprising: at least one foam layer including a plurality of cells,wherein at least 10% of the cells are closed cells, and solid layerscomprising HDPE on each side of the foam layer, and one or more solidlayers, comprising Ethylene vinyl alcohol (EVOH), each between the foamlayer and the solid layer, or between two of the solid layers, whereinthe film has an overall thickness equal to or greater than 8 mils, andthe film has an average Sheffield smoothness of less than 40, accordingto TAPPI T
 538. 3. A process of making the film of comprisingintroducing supercritical blowing agent, with an injection pressure ofmore than 240 bar at the concentration of less than 0.065 weightpercent, into a molten polymeric resin inside a mixing section of anextruder to form a mixture of blowing agent and molten polymer.